EP0156756A2

EP0156756A2 - Method and apparatus for feeding sheets, particularly fabrics from a stack

Info

Publication number: EP0156756A2
Application number: EP85630027A
Authority: EP
Inventors: Daniel Granot; Ahron Siev; Freddy Derfler; Fabrizio Servi; Ehud Armoza; Ephraim Sher; Boaz Eidelberg
Original assignee: State of Israel Ministry of Defence Raphael Armament Development Authority; State of Israel
Current assignee: State of Israel Ministry of Defence Raphael Armament Development Authority; State of Israel
Priority date: 1984-03-02
Filing date: 1985-02-28
Publication date: 1985-10-02
Also published as: EP0156756A3; CA1233847A

Abstract

A method and apparatus for feeding sheets, particularly fabrics, from a stack (S1) comprises an arrangement for: engaging the opposite edges of the upper sheet of the stack by a pair of restrainer members (16, 18), bringing a pick-up head (PH1) into engagement with the upper sheet of the stack (S1) while producing air streams from the pick-up head (PH1) directed outwardly across the opposite edges of the upper sheet of the stack, lowering the pick-up head (PH1) to depress the stack below the restrainer members (16, 18) whereby the air streams cause the opposite edges of the upper sheet of the stack (S1) to curl upwardly to clear the restrainer members (16,18), lifting the upper sheet from the stack (S1), and permitting the stack (S1), to rise so as to bring the next sheet into engagement with the restrainer members (16, 18).

Description

The present invention relates to a method and apparatus for feeding sheets from a stack. The invention is particularly useful for feeding sheets of fabric, and is therefore described below with respect to this application.
The feeding of paper, cardboard and similar sheets is relatively simple, and many such feeding devices have been developed and are in widespread use. The feeding of fabrics and similar types of limp and/or porous materials is considerably more difficult because of the limpness and porosity of such materials. in addition to their softness, roughness, compressibility and surface friction or adhesion. The foregoing properties of such materials introduce many problems which are difficult to overcome in an automatic handling system. Thus, the limpness and softness of these materials cause contacting surfaces to intermesh, making them difficult to separate; their limpness also makes lifting difficult; and their roughness causes the underlying sheet to be carried with the top sheet when moved transversely of the stack or pile. In addition, the threads at the edges of adjacent sheets often are entangled and not aligned. Vacuum devices for lifting such sheets are usually not effective because of the porosity of the sheets. Adhesives have also been found ineffective and are usually not desired because of the possibility of marking or damaging the sheets, A number of air-jet devices have been designed for this application, in which the air-jets produce a lift or flutter of the topmost sheet for separating it. Examples of the latter type devices are illustrated in USA Patents 3,877,695,' 3,796,455, 3,738,645, 3,647,202, 3,596,900, 3,539,177, 3,168,308 and 3,168,307; but even these air-type devices have still not been found entirely satisfactory.
An object of the present invention is to provide apparatus for feeding sheets from a stack, particularly fabrics or other materials having similar characteristics.
According to the present invention, there is provided sheet-feeding apparatus, comprising a horizontal table for supporting a plurality of sheets in a stack, and a pick-up head overlying said table and having air openings for producing air streams outwardly across opposite edges of the top sheet of the stack to curl upwardly such edges and thereby to separate them from the remainder of the stack, characterized in that said apparatus further comprises: a pair of restrainer members overlying-and engageable with said opposite -edges of the stack; the air streams produced by said pick-up head being effective to curl upwardly said opposite edges of the top sheet of the stack; and displacing means effecting relative displacement between said stack and said restrainer members in one direction such that the complete stack is displaced below said restrainer members and, after the opposite edges of said top sheet have been curled upwardly to clear said restrainer members, effecting relative displacement between said stack and said restrainer members in the opposite direction such that the opposite edges of the next underlying sheet of the stack are brought into engagement with the restrainer members.
The invention is hrerein described, by way of example only, with reference to the accompanying drawings wherein:

Fig. 1 is an end view illustrating one form of apparatus constructed in accordance with the present invention;
Fig. 2 in a side elevational view of the apparatus of Fig. 1;
Fig. 3 is an end view of one of the pick-up heads in the apparatus of Fig. 1;
Fig. 4 is a section along lines IV--IV of Fig. 3;
Fig. 5 is a fragmentary three-dimensional view of a portion of the pick-up head of Fig. 3;
Figs. 6a-6b illustrate different stages during the operation of the apparatus;
Fig. 7 is an end elevational view illustrating another form of apparatus constructed in accordance with the invention;
Fiq. 8 is n top plan view illustrating the apparatus of Fig. 7 but with the pick-up head and the restrainer members removed;
Figs. 9a-e are end views illustrating different types of nozzles that may be used for producing the air streams, Ftq. 9f being a top plan view of the nozzle of Fig. 9e;
Figs. 10a-e are side elevational views illustrating the nozzles of Figs. 9a-e, respectively;
Fig. 11 is an end elevational view illustrating another form of sheet feeding device constructed in accordance with the present invention;
Fig. 12 is a top plan view of the apparatus of Fig. 11 with the pick-up head removed;
Fig. 13 is a three-dimensional view illustrating a still further f6rm of sheet feeding apparatus constructed in accordance with the present invention;
Fig. 14 is a side elevational view illustrating a still further form of sheet separating and feeding apparatus In nccordance with the invention;
Fig. 15 is a top plan view of the apparatus of Fig. 14 but with the pick-up head removed;
Fig. 16 is a three-dimensional view illustrating a further form of sheet feeding apparatus in accordance with the invention particularly useful for also folding the sheet;
Fig. 17 is a three-dimensional view better illustrating the actual folding mechanism in the apparatus of Fig. 16;
Figs. 18a-18d are diagrammatical views illustrating the sequence of nteps performed by the apparatus of Figs. 16 and 17 during a folding operation;
Fig. 19 schematically illustrates a further improvement;
Fig. 20 schematically illustrates a still further improvement, Figs. 20a, 20b and 20c showing the operation of the ptck-up head when including this improvement;
Figs. 21 and 21a are top and sectional views, respectively, illustrating yet another improvement; and
Fig. 22 illustrates a modification of the improvement of Figs. 21 nnd 21a, Figs. 22a and 22b being diagrams helpful In understanding the modification of Fig. 22.

The apparatus illustrated in Fig. 1 is particularly useful for nnpnrnting and feeding sheets of fabric or similar materials from a stack or pile; actually, the illustrated nppnratus acts on two stacks S₁, S₂ simultaneously. Briefly, the apparatus comprises a base 2 supporting a horizontal table 4 adapted to.receive the two stacks S₁, S₂ of sheet materials.' Table 4 is mounted for vertical movement by means of a piston-cylinder drive 6 and is guided during its vertical movement by a sleeve 8, slideably received around a vertical post 10 supported by the base 2. The apparatus further includes a pair of pick-up heads PH₁, PH₂, supported on a common mounting member 12 having an attachment fixture, shown schematically at 14, for attaching same to a robot arm or the like (not shown) which feeds the sheets individually from the stacks S₁, S₂ to the desired locations for further processing, handling, storage or the like. Many types of attachment fixtures and robot arms or other transfer devices are known which can be used.
The apparatus illustrated in Fig. 1 further includes a pair of elongated, parallel restrainer members in the form of rods 16, 18 located to overlie the two stacks S₁, S₂ and to engage the opposite edges of the top sheet in each stack. Each of the opposite ends of restrainer rod 16 includes a U-shaped member 20 received over a bar 22 carried by a fixed support 24 to permit adjustment of the restraining rod (left to right in Fig. 2). A spring 26 interposed between bar 22 and member 20 releasably retains rod 16 in its adjusted position. A similar arrangement (not shown) is provided to permit adjustment of restraining rod 18.
Each of the two pick-up heads PH₁, PH₂ includes two pick-up devices PD_a, PD_b each overlying one of the two opposite edges of the top sheet in the respective stack. Fig. 2 illustrates the two pick-up devices PD_a, PD_b for head PH₁. Figs. 3-5 more particularly illustrate the construction of pick-up device PD_a. Pick-up device PD_b for head PH₁, and the two pick-up devices for the other pick-up head PH₂, are of the same construction.
As shown particularly in Figs. 3 and 4, pick-up device PD a includes a housing 30 having a connector 32 for connection to a tube 34 leading to a supply of pressurized air (not shown). Air is introduced through a bore 36 formed in the housing leading to an internal chamber 38 extending substantially the complete length of the housing. The housing is further formed with a plurality of openings 40 spaced along the length of chamber 38 for producing a plurality of air streams or jets substantially at a right angle to the outer face of the housing and spaced along its length.
A cylindrical member 42 is mounted on the front face of housing 30 by means of a bracket 44, such that the lower end of member 42 is substantially aligned with the axes of the air outlet openings 40. Thus, the air streams or jets are outletted from the latter openings substantially tangentially to the lower face of cylindrical member 42. Since this lower face curves upwardly, the air stream follows this curvature and thereby produces a force curling the respective edge of the top sheet of the stack upwardly. This is used for separating the top sheet from its stack, as will be described more particularly below with reference to the operation of the apparatus as illustrated in Figs. 6a-6d.
Housing 30 of each pick-up device further includes a pair of vertical bores each receiving a threaded bolt 50. Each bolt carries at its lower end a pin 52, 54 to project below the lower surface of the housing (Fig. 3). The pins 52, 54 are adapted to penetrate the top sheet during its separation from the stack. Pins 52, 54 may be of very small diameter since their purpose is not to pick up the top sheet of the stack, but rather merely to prevent its lateral displacement when it is picked up and transferred by air pressure, as will be described below.
The two pick-up devices PD_a, PD_b for pick-up head Pil1 are mounted on a common horizontal bar 60 and include means for adjusting the pick-up device along the length of the mounting bar to accommodate different size sheets. For this purpose, the end of housing 30 of each pick-up device is bifurcated to define two clamping jaws 62, 64 (Fig. 3) separated by a slot 66. A pin 68 is received within a bore formed in clamping jaw 62. The upper end of the bore is enlarged, and the lower end is threaded for receiving the lower threaded end 72 of pin 68. Pin 68 includes an enlarged head 74 bearing against the outer face of clamping jaw 62. Head 74 of the pin is fixed to a lever arm 76. It will thus be seen that when lever arm 76 is manually turned in one direction, pin 68 permits the two clamping jaws 62, 64 to spread apart so that the pick-up device may be adjusted along the length of the mounting arm 60; and when arm 76 is turned in the opposite direction, the two clamping jaws are drawn together to fix the pick-up device in position on the mounting arm.
The apparatus illustrated in Figs. 1-6 operates in the following manner:

First, the horizontal table 4 is loaded with the two stacks or piles S₁, S₂ of sheet materials to be handled, such as fabrics or the like. The two restraining rods 16, 18 are adjusted along bars 22 so that they are slightly inwardly spaced from and overlie the two opposite edges of the stacks S₁, S₂. The pick-up devices (PD_a, PD_b) of each of the two pick-up heads PH₁, Pil2 are then adjusted along their mounting bar 60, by turning lever arm 76 in one direction to permit the adjustment, and then in the opposite direction to fix the devices in proper position spaced slightly inwardly of the restraining rods 16, 18 for the two stacks.

After these preliminary adjustments have been made for the respective materials to be handled, the apparatus is operated according to the following sequence of steps:

a) Table 4 carrying the two stacks S1, S₂ is driven upwardly by the piston-cylinder drive 6, so as to cause the opposite edges of the top sheet of each stack to be engaged by the lower faces of the two restraining rods 16, 18 (Fig. 6a);
b) The two heads PH₁, PH₂ are driven downwardly to bring their pick-up devices into engagement with the top sheet of each stack between the restraining rods 16, 18, while pressurized air is applied via tubes 34 to the pick-up devices of the two heads, to produce air streams or jets outletted from the openings 40 tangentially to the lower faces of cylinders 42. The heads are then driven further downwardly to displace the stack downwardly so as-to move the stacks below, and out of contact with, the restraining rods 16, 18 (Fig. 6b); this lowering of the stacks is permitted by the air cushion formed by the piston-cylinder drive 6, which air cushion acts as a spring as schematically shown in Figs. 6a-6d
c) After the stack has been lowered below the restraining rods 16, 18, the air flow causes the opposite edges of the top sheet of each stack to curl upwardly, to clear the restraining rods 16, 18 (Fig. 6c). At this time, pins 52, 54 carried at the lower end of the pick-up devices have penetrated the top sheet (and perhaps one or more of the lower sheets) of the respective stacks.
d) The air flow is maintained through the outlet openings 52, 54, as the pick-up heads are moved upwardly so as to remove the top sheet of the respective stack, this being permitted because the opposite edges had been curved upwardly to clear restraining rods 16, 18. With this disengagement of the pick-up heads from the stack, the remainder of each stack is permitted to rise with table 4 by the air cushion formed by the piston-cylinder drive 6, whereupon the new top sheet of each stack is now engaged by the two restraining rods 16, 18, ready for a new cycle of operation.

The curling upwardly of the opposite edges of the top sheet to clear the restrining rods 16, 18 (Fig. 6c) usually requires a greater velocity of air than that required to hold the top sheet from the remainder of the stack (Fig. 6d). Accordingly, the air velocity applied to the pick-up devices may be higher for step Fig. 6c, (e.g., 4 atmospheres), and may then be lowered (e.g., to 2 atmospheres) for the step illustrated in Fig. 6d.
As indicated earlier, pins 52, 54 may be made of very small diameter since their purposes Is not to pick-off the top sheet of the stack, but rather merely to prevent lateral movement of the top sheet when picked-off by the air flow in the step of Fig. 6d. This is because the air flow applied to the opposite edges of the top sheet is in opposite directions but is not always equal, and therefore, there may be a tendency for the sheet to move laterally of its pick-up device during the transfer of the sheet. Such lateral movement is prevented by pins 52, 54.
The piston-cylinder drive 6 would be continuously or periodically adjusted to maintain a constant level between the top sheet of each stack with respect to the fixed restraining rods 16, 18. This drive, as indicated earlier, also serves as a cushion or yieldable means urging the table, and the stacks thereon, towards the restraining rods 16, 18 when the respective pick-up head is out of contact with its stack, as shown in Figs. 6a and 6d.
It will he appreciated that the apparatus san include various combinations, sizes and locations of pick-up heads according to the size, shape, weight, etc. of the sheets being handled.
The apparatus illustrated in Figs. 7 and 8 is particularly useful for separating and feeding sheets of fabric or similar materials having a very high tendency of entanglement. Fig. 7 illustrates these sheets in the form of a stack ST supported on a horizontal table 104, and a pick-up head PH overlying the table and movable toward it to engage an intermediate portion of the top sheet of the stack while leaving the opposite ends of the sheet free, and then away from the table to remove the top sheet of the stack. For this purpose, pick-up head PH includes a pick-up device PD1, PD2 at its opposite ends, each of which produces air streams directed outwardly across the opposite edges of the top sheet. The apparatus illustrated in Fig. 1 further includes a pair of elongated, parallel restrainer rods 116, 118; located to overlie the opposite edges of the top sheet in each stack, as in Fig. 1.
Insofar as described above, the apparatus illustrated in Fig. 7 operates as in Fig.1.
The apparatus illustrated in Figs. 7 and 8 further comprises one or more air nozzles 150, 152 located on the two opposite sides of stack ST and directed inwardly towards each other so as to produce air streams impinging against the stack. This causes the free ends of the uppermost sheets, and particularly the top sheet, of the stack to rise and flutter, thereby aiding in the separation of the top sheet by the pick-up head PH. Air nozzles 150, 152 are operated to produce the air streams while pick-up head PH depresses the stack below the restraining bars 116, 118 and applies its own air streams to curl the opposite ends of the top sheet upwardly to clear the restrainer bars; the flutter produced by the air streams from nozzles 150, 152 has been found to greatly aid in the separation of the edges of the top sheet from the edges of the underlying sheet.
Preferably, nozzles 150, 152 are also operated even before pick-up head PH engages the top sheet in order to cause this flutter to start then; and the operation of these nozzles is preferably continued even after the pick-up head starts to move, with the top sheet, away from the stack, such that the air streams produced by nozzles 150, 152 further aid in completing the separation of the top sheet from the underlying sheet during the movement of the top sheet away from the underlying sheet by the pick-up head.
It has been found that apparatus operating as described above can successfully separate fabric sheets having a very high tendency of entanglement between the fibers at their contacting faces as well as at their edges, something which, insofar as we are aware, has been successfully accomplished heretofore only by manual means. In addition, it has been found that providing the nozzles 150 and 152, and operating them as described above, also substantially reduces the required air flow rate for separating the fabric sheets, as compared to the air flow rate required without the air streams produced by nozzles 150, 152.
Nozzles 150, 152 may be oriented with respect to the ends of the stack ST at any desired angle about their horizontal axes, as shown in Fig. 7, or at any desired angle about their vertical axes, as shown in Fig. 8, depending upon the application, and particularly the characteristics of the sheet materials to be separated.
Figs. 9 and 10 are end and side views, respectively, illustrating a number of different types of openings which may be used for nozzles 150, 152 of Figs. 7 and 8. Thus, nozzle 150a includes a single circular opening 151a producing a single air stream of circular cross-section; nozzle 150b includes a plurality of circular openings 151b (in this case three openings in side-by-side relationship) producing a plurality of spaced air streams each of circular cross-section; nozzle 150c includes an opening 151c in the configuration of a short elongated slot for producing an air stream of rectangular cross section; nozzle 150d includes a tubular member 153d formed with an elongated slot 151d of substantial length, so as to produce a long air stream of rectangular cross-section; and nozzle 150e also includes a tubular member 153e, formed with a plurality of openings 151e to produce a plurality of air streams along a substantial length.
Figs. 11 and 12 illustrate a still further arrangement, wherein the nozzles outwardly of the restraining bars 216, 218 are constituted of a single tube or header 250 which is bent to provide two end legs 250a, 250b parallel to the opposite ends of the stack, the end legs being joined by an intermediate leg 250c extending along the front of the stack. All the legs are provided with openings for producing air streams, which thus impinge against the stack along its two opposite ends and also along its front edge. The air nozzle arrangement illustrated in Figs. 11 and 12 may also be operated as described above with respect to Figs. 7 and 8, namely before the engagement of the pick-up head with the top sheet of the stack, after this engagement while the pick-up head depresses the top sheet of the stack below the restraining rods while the pick-up head applies its own air streams to curl the opposite edges of the top sheet outwardly to clear the restraining rods, and/or during the pick-off of the top sheet from the remainder of the stack.
Fig. 13 illustrates a further arrangement, wherein the restraining rods (only rod 318 being shown) are also used for conducting the air streams to the nozzles, therein designated 352, which air nozzles are secured to their respective restraining rods. The nozzles 352 in the arrangement illustrated in Fig. 13 could also be operated as described above with respect to Figs. 7 and 8, or Figs. 11 and 12.
Figs. 14 and 15 illustrate a still further arrangement, wherein the retainer rods are also formed as air nozzles to produce air streams tending to curl the edges of the sheets of the stack. Fig. 14 illustrates only one retainer rod 416, this rod being formed of hollow, tubular construction and provided with a line of openings 417 along its length for outputting a plurality of air streams each having a component tangential to the-top sheet of the stack. The curved surface of tubular member 416 facing the free end of the top sheet of the stack applies a force to that sheet tending to curl its free edge according to the curvature of this curved surface. Tubular member 416 is adjustable about its horizontal axis, as shown by the arrows in Fig. 14, in order to vary the angular position of its air output openings 417 with respect to the top sheet of the stack, and thereby to vary the tangential component of force applied to the free edges of the stack tending to curl them about the outer face of member 416.
The apparatus illustrated in Figs. 14 and 15 includes a plurality of further nozzles 450 extending along the respective end of the stack and coupled together by a common header 453, for applying air streams to the respective end of the stack in the same manner as described above.
It will be appreciated that the opposite end of the stack also includes a tubular restrainer member corresponding to member 416, and a plurality of further air nozzles corresponding to air nozzles 450.
Figs. 16 and 17 illustrate a further form of sheet feeding apparatus, which apparatus may also be used for folding the ends of the sheet. Thus, the illustrated apparatus includes a horizontal table 504 for receiving a stack of sheets (or only one sheet), and a pair of tubular rods 516, 518 overlying the opposite ends of the sheet. Tubular members 516, 518 are of similar construction as tubular member 416 in Figs. 14 and 15, and are formed with a plurality of air outlet openings 517, 519, respectively, directed towards the outer edges of the sheet so as to apply a tangential component of force thereto, causing the outer edges to curl upwardly to conform to the curvature of the members 516, 518. In this arrangement, the outer edges of the sheet are preferably curved more than 90° so as to overlie the intermediate portion of the sheet, as shown in Figs. 17 and 18b. Tubular members 517, 519 are supported by a carriage 520 (Fig. 16) which can move these members to their operative positions illustrated in Figs. 16 and 17 (also in Figs. 18a, 18b), or to a retracted position out of alignment with the sheet, this being schematically shown by the broken lines in Fig. 18c.
The apparatus illustrated in Figs. 16 and 17 further includes presser means in the form of two depending pressure members 526, 528, overlying, and in alignment with, the two air stream producing members 516, 518. The two pressure members 526, 528 are carried by -a common carriage 530 which is also movable either to a retracted position illustrated in Fig. 16, or to an extended, operative position overlying the folded ends of the sheet, as shown in Fig. 17.
Figs. 18a-18b illustrate the sequence of operations of the apparatus of Figs. 16 and 17. Thus, as shown in Fig. 18a, the air stream producing members 516, 518 engage the sheet on the table and produce an air stream tending to curl the edges of the sheet around the outer face of members 516, 518 (Fig. 18b). Carriage 530 is then actuated to bring its pressure members 526, 528 downwardly against the curled edges of the sheet; at this time members 516, 518 are withdrawn (Fig. 18c), whereupon the pressure members 526, 528 are moved further downwardly to press the ends of the sheet against its intermediate portion to thereby produce a fold at each of its opposite ends.
The apparatus illustrated in Figs. 16 and 17 is preferably also provided with the outboard nozzles, corresponding to nozzles 150, 152, to aid in curling the edges of the sheet around the tubular members 516, 518, and also to aid in removing the sheet from the stack as described above with respect to Figs. 7 and 8.
The apparatus illustrated in Fig. 19 includes a similar pick-up head, generally designated 600, as in Fig. 1; a table 604 for supplying a stack 605 of the sheets to be fed by the apparatus; and a piston-cylinder drive 606 for raising and lowering table 604. The movements of the table are guided by sleeves 608 fixed to the base (not shown) of the apparatus which sleeves receive vertical posts 610 fixed to table 604. Overlying table 604 are a pair of restrainer members 616, 618 located to engage the opposite edges in the top sheet of the stack.
In the arrangement illustrated in Fig. 19, the pick-up.head 600 is driven towards and away from table 604 by a piston-cylinder drive 620. In addition, the operation of the table drive 606 is synchronized with the operation of the pick-up head drive 620 by a synchronized controller, schematically shown at 622, such that when the pick-up head 600 is driven downwardly to engage the top sheet of the stack 605, table 604 is also driven downwardly by its drive 606 to reduce or eliminate the compression of the top sheet caused by the engagement thereof by the pick-up head. In other words, the downward movement of the pick-up head is accompanied by a downward movement of the table 604 so that there will be little, if any, compression of the top sheet of the stack 605 at the time of engagement thereof by the pick-up head 600.
A preferred manner of operation is as follows: Controller 622, at the time it actuates drive 620 to lower the pick-up head 600, also actuates drive 606 to lower table 604, but at a lower speed, so that the pick-up head 600 catches up and makes contact with the top sheet of the stack 605 at the lower end of the- head and table strokes when there is very little, if any, relative motion between the two at the instant of contact; similarly, when controller 622 actuates drive 620 to raise pick-up head 600, it also actuates drive 606 to raise the table 604, but at a lower speed, to permit the pick-up head to reach its higher level above the table. Thus, the pick-up head 600 and table 604 operate at different speeds; the compression effected by the pick-up head 600 with respect to the stack 605 is determined by the differential speed at the time of contact of the head with the top sheet of the stack. Such an arrangement has been found particularly effective with respect to fabric sheets having a very high tendency of entanglement, in that it reduces the internal stresses in the fabric sheets and thereby their tendency to adhere to each other.
The apparatus illustrated in Fig. 20 is similar to that of Fig. 19, in that it includes a pick-up head, generally designated 700, movable with respect to a table 704 adapted to contain a stack of sheets 705 underlying a pair of restrainer members 716, 718, the table and pick-up head including drives 706 and 720, respectively, and a synchronized controller _'722 for controlling their operations.
Fig. 20, however, further includes a pressure plate, generally designated 730, carried by pick-up head 700 centrally thereof, and a drive 732 for the pressure plate. The operation of the pressure plate drive 732 is also controlled by controller 722, so as to produce the sequence of operations illustrated in Figs. 20a, 20b and 20c, as follows:

As pick-up head 700 approaches the top sheet of the stack on table 704, pressure plate 730 is in its upper retracted position, above the lower faces of the pick-up head 700 (Fig. 20a). After pick-up head 700 has come into contact with the top sheet of the stack, drive 732 of pressure plate 730 is actuated to move the pressure plate downwardly until it reaches (Fig. 20b) and passes (Fig. 20c) the level of the lower face of the pick-up head 700, to thereby compress the center of the stack. At this time, the outer edges of the stack are also below the restrainer members 716, 718, and therefore the opposite edges of the top sheet of the stack are free to curl upwardly, under the influence of the air streams produced by the pick-up head 700, to clear the restrainer members. Since the pressure plate 730 at this instant has displaced the center of the stack further downwardly than the outer edges, this arrangement better permits the opposite edges of the top sheet to curl upwardly to clear the restrainer members 716, 718 before the machine operation continues wherein relative displacement between the stack and the restrainer members is effected in the opposite direction.

_Fig. 21 illustrates a modification in the construction of each of the two pick-up devices included in the pick-up head. The illustrated pick-up device, generally designated 800, is the one acting on the right side of the top sheet of the stack. It includes a nozzle 830 formed with a plurality of air outlet openings 840, corresponding to housing 30 and air outlet openings 40 in the apparatus of Fig. 3. Each pick-up device further includes a rod of cylindrical cross-section 842, providing a surface curving outwardly away from the table, similarly to rod 42 in Fig. 3. but of smaller diameter than that rod.
Each pick-up device further includes a shield 844 extending between the air openings 840 in nozzle 830 and rod 842, the outer end of the shield being slightly spaced from rod 842 to provide a flow path 846 (Fig. 21a) for the air streams issuing from nozzle 830.
As shown in Fig. 21a, shield 844 guides the airflow to be tangential to the outer face of rod 842 in order to produce the forces tending to curl upwardly, around the rod, the outer edges of the top sheet of the stack. Shield 844 also acts to prevent the top sheet of the stack from blocking the air openings 840 in nozzle 830. The arrangement illustrated in Figs. 21 and 21a, therefore, increases the reliability of the apparatus and prevents a sheet from blocking the airflow which 'curls the edges of the top sheet of the stack to clear the restrainer members (e.g., 716, 718 in Fig. 20).
Fig. 22 illustrates a further modification that may be included in the pick-up device of Fig. 21 in order to further increase its reliability particularly when feeding fabrics having a very high tendency of entanglement between sheets. Thus, the pick-up device in Fig. 22, generally designated 900, also includes a nozzle 930, a cylindrical rod 942, and a shield 944. In Fig. 22, however, rod 942 is carried at the end of an arm 950 which is movable by a piston-cylinder drive 952 so as to move rod 942 either to an initial, inoperative position, as shown by full lines in Fig. 22, or to an operative position as shown by broken lines in Fig. 22.
In the inoperative position of rod 942, the rod has no significant influence on the air streams from nozzle 930, so that such air streams produce a fluttering action on the top sheet 905 of the stack as shown in Fig. 22a. This is the position of rod 942 when the pick-up head is distant from the top sheet; the increased fluttering action better separates the edges of the top sheet from the underlying sheet,-as shown in Fig. 22a.
However, as or after the pick-up head engages the top sheet 905 and displaces the complete stack below the restrainer members (e.g. 616, 618, Fig. 19), drive 952 is actuated to move rod 942 to its operative position (Fig. 22b), whereby its presence in the air stream increases the forces tending to curl the outer edges of the top sheet 905 of the stack around the rod and thereby to clear the restrainer members.
Rod 942 and arm 950 may be replaced by a substantially planar sheet which is curved at its outer tip into a semi-cylindrical configuration, similar to the configuration illustrated by the top sheet 905 in Fig. 22b.

Claims

1. Sheet-feeding apparatus, comprising a horizontal table for supporting a plurality of sheets in a stack, and a pick-up head overlying said table and having air openings for producing air streams outwardly across opposite edges of the top sheet of the stack to curl upwardly such edges and thereby to separate them from the remainder of the stack, characterized in that said apparatus further comprises: a pair of restrainer members overlying and engageable with said opposite edges of the stack; the air streams produced by said pick-up head being effective to curl upwardly said opposite edges of the top sheet of the stack; and displacing means effecting relative displacement between said stack and said restrainer members in one direction such that the complete stack is displaced below said restrainer members and, after the opposite edges of said top sheet have been curled upwardly to clear said restrainer members, effecting relative displacement between said stack and said restrainer members in the opposite direction such that the opposite edges of the next underlying sheet of the stack are brought into engagement with the restrainer members.

2. Apparatus according to Claim 1, wherein: said apparatus includes yielding means urging said table toward said restrainer members to bring the opposite edges of the top sheet of the stack into engagement with the lower faces'of the restrainer members; and said displacement means lowers said pick-up head into engagement with said stack and depresses said stack against said yielding means in order to lower said stack to cause the opposite edges of the top sheet to curl upwardly and to clear said restrainer members.

3. Apparatus according to either of Claims 1 or 2, wherein said restrainer members are in the form of elongated rods.

4. Apparatus according to any one of Claims 1-3, wherein said pick-up head removes said top sheet from the stack by maintaining said air streams to cause the sheet to adhere to the pick-up head.

5. Apparatus according to Claim 4, wherein said pick-up head includes a pin adapted to penetrate said top sheet and thereby to prevent its movement laterally of the pick-up head when removing same from the stack.

6. Apparatus according to any one of Claims 1-5, further including air nozzles located on opposite sides of the stack and directed inwardly towards each other so as to produce air streams impinging against said stack to cause the free ends of the top sheet to flutter with respect to the underlying sheet of the stack, thereby aiding in the separation of the top sheet from the stack by said pick-up head.

7. Apparatus according to any one of Claims 1-5, wherein said air openings in said pick-up head are formed in a nozzle and are spaced along the length of, and include a curved surface facing, the free ends of the top sheet, such that the nozzle produces air streams tending to curl said free ends of the sheet upwardly around the nozzle curved surface; and means for pressing said curled ends of the sheet against an intermediate portion of said sheet to produce a fold therein.

8. Apparatus according to Claim 1, further including a table drive for lowering and raising said table with respect to said restrainer members, said displacing means effecting relative displacement between said stack and said restrainer members comprising a head drive for lowering and raising said pick-up head, and synchronizing means synchronizing the operation of said table drive and said head drive such that the pick-up head is driven downwardly to engage the top sheet of the stack, and at the time of said engagement, said table is also driven downwardly to reduce or eliminate the compression of the uper sheet caused by the engagement thereof by the pick-up head.

9. Apparatus according to Claim 1, further including a pressure plate carried by said pick-up head centrally thereof, a drive for said pressure plate, and synchronizing means effective, when said stack is displaced below said restrainer members, to actuate said drive and to cause said pressure plate to press the center of the stack further downwardly below the restrainer members, to thereby better permit the' edges of the top sheet of the stack to curl upwardly to clear said restrainer member, before effecting relative displacement between said stack and the restrainer members in said opposite direction.

10. Apparatus according to Claim 1, wherein said pick-up head comprises a curved surface curving upwardly away from said table, and a shield between said air openings and said curved surface preventing the top sheet of the stack from blocking said air openings.